An electronic package typically includes a circuitized substrate with one or more active devices attached thereon. The use of attach materials, such as an adhesive, is common in electronic packaging applications for attaching the devices to the substrate, particularly in Ball Grid Array (BGA) packages.
BGA packages are a relatively recent development in the electronic packaging industry, replacing current products such as Quad Flat Packs (QFP). The main difference is the connection system to the printed circuit board (PCB), also called second level attachment, that is made through eutectic tin-lead solder alloy balls arranged in a matrix layout on the bottom side of the BGA package, instead of metal leads placed along the peripheral corner of the plastic component body. BGA and QFP packages are described in “Circuits Assembly (USA)—Vol. 6, No. 3, March, 1995 pages 38-40”.
U.S. Pat. No. 5,574,801 discloses a method of inspecting an array of solder balls used as connections in integrated circuit modules. The method checks the deviation of the balls from a best fitting plane through the balls in order to ensure that the array is flat. If the array is not flat, then one or more of the balls may fail to make an electrical connection with the PCB.
In order to check that all of the electrical connections have been made between the balls and the PCB, the completed assembly may be inspected with the use of X-Rays. The size and location of the connections, especially those internally positioned, do not allow inspection with the naked eye. However, it can be very difficult to determine, when inspecting from above with X-Rays, whether a solder connection has formed successfully or not. A round dark image appears of the ball and corresponding circular pad whether or not a solder connection is made, making detection difficult.
One solution to this problem is to use X-Ray Laminography. An X-Ray Laminography machine can produce synthetic X-Ray sections through the connection, allowing the 3-dimensional shape to be assessed and a determination made as to whether a good solder connection has been made. However, such X-Ray Laminography equipment is relatively expensive.
It is believed, therefore, that an enhanced pad design for an electronic package in which a simple X-Ray process would readily identify those connections which have not been made, without recourse to an X-Ray Laminography machine, would represent a significant advancement in the art.